The long term goals of this project are to understand the immunobiology of asthma and allergic diseases. In the current application, we propose to examine the characteristics and function of Natural Killer T (NKT) cells, which we and others have shown to play a critical role in the regulation of asthma. NKT cells comprise a small subset of lymphocytes that rapidly produce large amounts of cytokines, that express a conserved or invariant T cell receptor (TCR), and that potently regulate immune responses (the development of colitis, type II diabetes, infectious diseases, cancer and tolerance). We recently showed that NKT cells are required for the development of airway hyperreactivity (AHR), a cardinal feature of asthma, in a mouse model of allergic asthma and in a mouse model of air pollution-associated asthma, and that NKT cells are present in the lungs of human patients with severe asthma. Our current proposal is designed: 1) to demonstrate that NKT cells are present in the lungs of patients with severe asthma but not in the lungs of nonasthmatic individuals, to determine the specific conditions that are associated with increased numbers of NKT cells in the lungs of patients with asthma, and to use novel molecular methods to identify previously overlooked microbes in the lungs that might express glycolipids and that could stimulate the expansion of NKT cells in the lungs. 2) to identify glycolipids present in common allergens that activate NKT cells thereby causing asthma. 3) to examine glycolipids that specifically inactivate NKT cells, as potential therapy for asthma. We have assembled an outstanding group of talented investigators including an internationally known lipid biochemist, who will assist us in analyzing glycolipid fractions of common antigens, expert bronchoscopists, and experts in using sensitive molecular methods to identify bacterial species in the lungs. We have exciting preliminary data in mouse models demonstrating the presence of distinct subsets of NKT cells in allergic asthma versus oxidative-stress induced asthma, that activation of NKT cells in non-human primates results in AHR, that the lungs of asthmatics contain previously unappreciated microbes, which could activate NKT cells, and that glycolipids purified from Aspergillus can specifically activate NKT cells. The proposed studies therefore, are likely to provide very fundamental information regarding the mechanisms by which NKT cells are involved in the pathogenesis of asthma. We believe that our studies of NKT cells in asthma will provide further evidence of their important role in asthma, significantly alter our understanding of the pathogenesis of asthma, and lead to new strategies that target NKT cells, as a greatly improved therapeutic approach for asthma. PUBLIC HEALTH RELEVANCE The results of these studies will have a direct impact on the treatment of asthma and allergy. Asthma represents a significant public health problem, as it affects 10-15% of the general population, and its prevalence has doubled over the past two decades. As a result, asthma has reached epidemic proportions, and current health care expenditure for asthma in industrialized countries is enormous. We are proposing new paradigms for the pathogenesis of asthma, and these new paradigms should lead to an improved understanding of asthma and to important novel therapies for asthma and allergy.